It's all right, I've sorted it now. What I didn't tell you is that as well as my On Mouse Down event I have a corresponding On Key Down event. I'd forgotten either to exempt the F4 key or to add the 'SendKeys "{F4}"' instruction to this:
Code:
If Not KeyCode = vbKeyF4 Then
If Me!Status.Value = "Cancelled" Then
MsgBox "You cannot amend a record for a cancelled document." _
, vbInformation
SendKeys "{F4}"
End If
End If
Without the 'SendKeys "{F4}"' instruction, the dropdown list is left open. Without the line 'Not KeyCode = vbKeyF4', the 'SendKeys "{F4}"' instruction in the other event creates an eternal loop. D'oh!
Sorry for littering your website with these petty issues.